Low-alloy corrosion-resistant steel



Fetenteci it inr,

w. c conosion-nssis'senn sense 5." Vnnderh This invention relates to low-olloy coonresistont steels, and it is pertirly corned with the production of e, steel of this type which is characterized by bovine exceptionally increased resistance to both fresh wster utmospheric corrosion. Insofer as is known, prior art steels of this type, while resistant to atmospheric corrosion, are not sppreciebly more resistant to fresh water corrosion than ordinary It has been found that the steel presently disclosed, when in contact with fresh wster, loses only about one-half the weight in a. given'period of time as do the plsin carbon or co-besrihs steels. In eddition, its loss in the atmosphere is only about one-third that of the plsin carbon steel, or two-thirds'thet of the copper-bearing steel.

This new steel is characterized by the following composition:

it is to be noted that the shove gives u nether exect snelysis best suited to its economical menu fecture by the open hearth, and one of breeder range that represents the variations thet one possible while still retaining the stecls unexpectedly high resistsnoe to fresh. water end atmospheric corrosion. it is to he no that the steel hesits resistance to both these types of corrosion. it might also be mentioned their the steel possesses its corrosiomresistent cherecteristics regardless of whether it is nest-treated.

In further enplenetion of the ysisoi the steel, it is to be understood that it is very dimcult, and sometimes undesirable, to provide on extremely low cnrbon content. The steels carbon may go as high as 10% without detracting from its qualities. The manganese and silicon are in- I cluded solely to permitthe manufacture oi the steel in accordance with good steel-making practices, but neither of these elements should exceed the stated amounts. The sulphur should be kept below 04%, as is customary in any good steel.

components thet actively contribute to the unexpec cteristics of the steel appear to be, in port, its phosphorus content, which incresses the atmospheric corrosion resistance of the steel without appreciably lessening its corrosion resistance to water; providing the stated phosphorus limits are observed. The copper also functions to improve the atmospheric corrosion resistance without introducing trouble of its own end without making the steel expensive to manuiscture, it being understood that, here again, the

limit stated should be observed. As to chromium, the content advanced rs to be the minimum required if the steel. is to have its extraordinary good resistance to fresh water corrosion. At the same time, it does not detract from the function of the phosphorus the copper. The upper limit of the chromium is set by the type of the new steel, it being understood that it should not exceed that taking the steel out of its low-alloy classification and placing it among the highelioy, end the more expensive, steels. It is commonly reco that s low-alloy steel should not contain more than about 3% chromium, beceuse of the emense attendant higher percentsees.

The titonium content of the steel functions to elite the necessity ior on expensive heattreetment, the steel having practically the same insistence to corrosion whether it is heat-treated or not. A stated amount of titanium, that is to sey, e. titanium. content proportioned to the carbon content as described, insures the steel having its menimum resistance to fresh water corrosion, regardless of the fact that it contains carbon either because of economicol reasons or because the carbon is needed to odd strength to the steel.

It is to be noted that the steel contains no nickel, this element 1.1- 1; neither needed nor desired. This is of importance, since, in times of war, nickel is e'metel of extreme strategic importence, it representing s-msteriel that must be imported to this country.

So far as is known, the inventors of other steels have pmd little attention to the fact that a. steel which may resist corrosion relatively satisfactorily from other media, is frequently subject to easy corrosion attack when exposed to fresh water. The atmospheric corrosion problem has been recognized, but it has remained uncoupled with the just-named type of corrosion. In the case of certain types of structures, such as steel barges which are exposed to both fresh water and atmosphere, a. steel having the exceptionally high resistance to both types of corrosion, such as is V possessed by this new steel, represents a material of considerable value. Such a material has been heretofore unavailable.

In closing, it might be mentioned that the new steel has adequate strength. Thus, physical tests applied to a sample of steel having the described composition showed that it had an ultimate strength of 65,100 pounds per square inch, with an attendant elongation in two inches of 19.5%.

I claim:

1. A steel of the low-alloy type and which is characterized by increased resistanceto both fresh water and atmospheric corrosion, said steel containing not. morethan .10% carbon, from .20 to .40% manganese, from .05 to .10% phosphorus, less than .04% sulphur, not more than .10% silicon, from .20 to .40% copper, from 1.75% to 3% chromium, about four times its carbon content'oi titanium, and with its balance substantially all iron,

2. A steel of the low-alloy type and which is characterized by increased resistance to both fresh water and atmospheric corrosion, said steel containing from .05 to .10% carbon, about .30% manganese, about .07% phosphorus, less than .04% sulphur, not more than .10% silicon, not

- less than 20% copper, from 1.75% to 3% chrolow-alloy.

mium and titanium to the amount of about four times said carbon content, said steel being otherwise iron, and said copper and chromium not being in excess of what qualifies said steel as CLIFFORD P. LARRABEE. 

